High rate activated sludge

Dryden, E.E. Barrett, P.A. Kissinger, J.C. Eckenfelder, Jr., W.W. High rate activated sludge treatment of fine chemical wastes. Sewage Ind. Wastes 1956, 29, 193. 

Other variations of activated sludge such as deep shaft high-rate activated sludge and sequencing batch reactor (SBR) have been used for refinery wastewater treatment. A refined deep shaft process has been installed and in operation at the Chevron refinery in Burnaby, British Columbia, Canada, since 1996 [45]. In the course of a recent wastewater treatment upgrade, a BP refinery on the eastern Australian coast converted an existing lagoon to an SBR system [46]. 

Completely-mixed aerated system (Figure 11.4) High rate activated sludge... 

High-rate filtration Oxidation, see Activated sludge. High-rate filtration. Trickling filter Reduction, see Anaerobic digestion Phenol removal... 

A description is given of a unique solution for the problems of overloaded conventional activated sludge systems. A high-rate dissolved air flotation (DAF) clarifier is applied in series between the... 

The primary distinguishing feature of the improved activated sludge treatment system is that high-rate DAF is the secondary clarifier for separation of suspended solids from the activated sludge aeration basin effluent, as opposed to secondary sedimentation alone in a conventional activated sludge system. 

In Section 27.2, the principles of a DAF unit and the entire improved activated sludge wastewater treatment system are disclosed in detail. The economic use of secondary flotation in the improved system requires only a relatively inexpensive high-rate DAF cell that is commercially available. The consulting engineers should understand such principles for the selection of an appropriate DAF unit and for the optimization of the entire improved wastewater treatment system. 

Under the high-rate conditions, the fluid remains approximately 2 hours in the aeration basin, and the BOD of feed is reduced between 50 and 70%. When maximum conversion is desired, over 95% of the BOD can be removed. This is termed an extended activated sludge process, and the average residence time is at least 18 hours. The conventional conditions are a compromise, with 90% of the BOD being removed and the fluid being detained around 5 hours.34 Table 16-3 gives the design information for these systems. 

The fate of hormones in urban WWTP has been abundantly documented. Several studies reported high removal rates for hormones from the liquid phase of sewage, particularly in those WWTP using activated sludge processes. For instance, removal rates of 40-96%, 40-100%, 40-96%, and 40-98% for, respectively, El, E2, E3, and EE2 were reported in WWTP all around the world. Nevertheless, residual hormone concentrations of < 0.3-100 ng L 1 of El, < 0.2-20 ng L 1 of E2, < 1-275 ng L 1 of E3, and < 0.3-7.5 ng L 1 of EE2 have been detected in treated effluents, which shows that hormones were not completely removed by the treatment processes [82, 84, 86, 90, 95-97]. 

Nitrate and oxygen also may play an important role in determining the rate of azo dyes reduction. Wuhrmann et al. demonstrated that obligate aerobes might actually decolorize azo dye compounds under temporary anoxic conditions. However, high nitrite concentrations in the mixed liquor of activated sludge plants could significantly inhibit dye removal. 

Depending on the wastewater treatment, removal rates can differ [46 9]. Moreover, for compounds of the same pharmacotherapeutic group, such as p-blockers, highly variable removal rates were obtained when the same treatment procedure was used. Activated sludge process lead to a significative removal efficiency for betaxolol, bisprolol, carazolol and metoprolol (65-90%) [49, 50],... 

A relatively new design of a high-rate DAF unit uses a shallow bed system (Supracell) with only 3 minutes of retention time and operated at an overflow rate of 140Lpm/sqm (3.5 gpm/sq ft) [42]. This unit has been used for industrial and municipal wastewater treatment and offers lower capital cost and headroom requirements. It was installed at a petrochemical complex in Texas as a secondary clarifier to improve the operation and the capacity of an existing activated sludge system [43]. In recent years, nitrogen has replaced air in covered DAF systems because of the potential for explosion. These systems are called dissolved nitrogen flotation (DNF) systems. The operations of DAF and DNF are similar. 

Activated sludge is the most common biological treatment process because of the high rate and degree of organic stabilization possible. It is widely used in treating refinery wastewater [5]. 

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